The invention relates to a sealing tool for heat-sealing a pull-off lid onto a container, a tearing-open tab for pulling the lid off by hand being formed on the lid.
With pull-off (peelable) lids for sterilizable and reheatable containers made of barrier plastic or another composite material containing aluminum (for example, STERALCON trays), for example for foodstuffs, problems arise as a result of contradictory requirements. Steralcan is a registered trademark of Alusuisse Swiss Aluminium Ltd. On the one hand, very firm seals must be obtained, in order to withstand the high internal pressures occurring during sterilization and, above all, during reheating in a water bath. On the other hand, the lid should be easy to open by hand.
To obtain the good closing properties mentioned, high sealing temperatures and sealing pressures have to be used during the closing. This leads to so-called sealing fold-back, especially in a sealing layer located on the underside of the lid, specifically both on the container inside and on the container outside. Such sealing fold-back on the inside of the container on the one hand improves the closure safety and is thoroughly desirable; on the other hand, however, it results in excessively high tearing-open forces during the pulling off (peeling), which make tearing open much more difficult and sometimes even impossible.